1. Technical Field
The present invention is generally directed to an improved integrated circuit design. More specifically, the present invention is directed to a system and method for increasing wiring channels/density under dense via fields of integrated circuits of a computer card.
2. Description of Related Art
Current printed circuit board constructions require one or more external conductive layers, e.g., circuitry and/or pads for mounting components thereon, and, given today's increased functional demands, a plurality of internal conductive planes, e.g., signal, power and/or ground. To provide effective interconnections between components and the board's conductive circuitry and pads, the use of through holes has been adopted wherein several such holes are passed through the board and electrically coupled in a selective manner to internal and external conductive elements. Such holes typically include a conductive, e.g., copper, layer as part thereof which in turn contacts the also typically copper circuitry and pads.
The term “through hole” or simply “hole” as used herein is meant to include both conductive and non-conductive apertures which may extend entirely through the circuit board or only partly there-through (such holes are often called “vias” in the art), including between two or more internal layers without being externally exposed. Examples of various circuit board structures which include the use of holes of these types and various methods of making such holes in circuit boards are defined in several published documents, including the following U.S. Letters patents, issued on the dates identified:
4,017,968WeglinApr. 19, 19774,319,708LomersonMar. 16, 19824,704,791Chellis et alNov. 10, 19875,450,290Boyko et alSep. 12, 19955,451,722GregoireSep. 19, 19955,487,218Bhatt et alJan. 30, 19965,557,844Bhatt et alSep. 24, 19965,571,593Arldt et alNov. 5, 19965,662,987Mizumoto et al.Sep. 2, 19976,609,296Farquhar et al.Aug. 26, 2003
Printed circuit boards of the aforementioned type are particularly adapted for having one or more (usually several) electrical components, e.g., semiconductor chips, capacitors, resistors, etc., mounted on an external surface thereof and coupled to various, selected internal conductive planes within the board's dielectric substrate. As demands for increased levels of integration in semiconductor chips and other electrical components continue, parallel demands call for concurrent increased functional capabilities, e.g., increased circuit densities, in printed circuit boards adapted for use with such components. Such demands further emphasize the growing need for more closely spaced electrical components on the board's outer surfaces. For those boards possessing greater functional capabilities and therefore which use several through holes therein, it is highly desirable to position the electrical components directly over the holes to maximize board real estate while assuring a compact, miniaturized final board product.
For any circuit board, or card, that uses an area array package, or other dense via field, the cost of the printed circuit board is directly determined by the strategy for wiring escape and the number of layers that are needed for the escape. As improvements in circuit technologies require increased numbers of wiring channels and increased wiring densities in circuit boards, techniques for increasing the wiring channels/densities have been developed. In order to address wiring congestion issues on circuit boards, typical solutions involve adding additional layers to the circuit board thereby increasing the amount of wiring channels available. However, adding additional layers to the circuit board increases the base cost of the printed circuit board. Other solutions use thinner wiring to escape under the module which detracts from the yield and increases the cost.
Thus, it would be beneficial to have a system and method for increasing the wiring channels/density under dense via fields of a circuit board without increasing the cost of the printed circuit board.